The Transmission Control Protocol/Internet Protocol (TCP/IP) does not consider the case that a topological location of a terminal will change in the initial design, i.e., the TCP/IP protocol itself does not support mobility. In a conventional TCP/IP network environment, the IP provides a routing function to the Internet. It allocates logical addresses i.e., IP addresses, to all nodes (including hosts and routers), and an IP address is allocated to each of the ports of each host. An IP address includes a network prefix portion and a host portion, and IP addresses of all hosts on the same link usually have the same network prefix portion and different host portions. This makes the IP be able to perform route selection based on a network prefix portion of an IP address of a destination node, thereby allowing the router to save a simple network prefix route in order, rather than save a separate route for each host. In this case, due to the use of a network prefix route, when the node is handed over from one link to another link without changing its IP address, the node is impossible to receive a data packet on the new link, thus not being able to communicate with other nodes.
With the dramatic increase in user demand for mobility and information, more and more people want to access to the Internet at a high-speed in the motion process, acquire on-demand information, and complete what they want to do. Therefore, the mobile Internet has become the future development direction of the Internet, but the defect that the conventional TCP/IP protocol does not support the mobility makes mobility management of the mobile node become a major problem faced by the mobile Internet.
In order to solve the problem of mobility management, popular mobility management technologies in the industry, such as Mobile IP (MIP), Proxy Mobile (PMIP) etc., support mobility of a terminal by means of introducing a fixed anchor. For example, the MIP protocol uses a Home agent (HA) as an anchor, and the PMIP protocol uses a Local Mobility Anchor (LMA) as an anchor.
FIG. 1 illustrates logical architecture of the PMIP protocol, including Mobile Nodes (MNs), i.e., MN1 and MN2, corresponding Mobile Access Gateways (MAGs), i.e., MAG1 and MAG2, and an LMA. The MAG is a first hop router MN, and its primary function includes allocating a Care of address (CoA) to the MN when the MN accesses and substituting the MN to perform PMIP binding with an anchor LMA of the MN. The LMA is used as an anchor of the MN, and its primary function includes allocating a Home of Address (HoA) to the MN and processing the above PMIP binding. The main purpose of performing PMIP binding between the MAG and the LMA is to make both parties to know addresses of each other, i.e., the above CoA and HoA, and store the addresses locally. In addition, in the process of performing PMIP binding, a bidirectional tunnel is established by the MN between the MAG and the LMA. It should be noted that, an IP address finally acquired by the MN is the HoA allocated by the LMA to the MN. In a typical network deployment, the MAG is generally located in the lower location of the topology, such as an edge of the metropolitan area; and the LMA is generally located in a higher location of the topology, such as a core part of the province network. In practice, the MAG and the LMA are often connected via a multi-hop router.
The mobility management of the PMIP protocol is embodied in that as the MN moves, the currently connected MAG can be changed, while maintaining the IP address of the MN (i.e. HoA) unchanged, that is the MN is always anchored in the local mobility anchor LMA which is initially registered. When the MN is handed over to a new mobile access gateway MAG, instead of the MN, the MAG registers a new PMIP binding with the anchor LMA and updates the new PMIP binding, and establishes a bidirectional tunnel between the anchor LMA and the new MAG to forward uplink and downlink data of the MN.
As shown in FIG. 1, a packet forwarding path between the MN1 and the MN2 is MN1<->MAG1<->LMA<->MAG2<->MN2. Packets transmitted by the MN1 to the MN2 arrive firstly at the MAG1, the MAG1 performs tunnel encapsulation on the packets and transmits the packets to the LMA through a tunnel between the MAG1 and the LMA, the LMA decapsulates the packets, re-encapsulates the packets, and transmits the packets to the MAG2 through a tunnel between the LMA and the MAG2, and the MAG2 decapsulates the packets and then forwards the packets to the MN2. The packets transmitted by the MN2 to the MN1 are forwarded in the same way. With the above method, the data between MN1 and MN2 always needs to be forwarded by a fixed anchor LMA, the data transmission path is not an optimal path, and decapsulation and re-encapsulation processes need to be performed by the LMA on the packets in the transmission process, which causes large delay and packet loss in the data transmission. A waste of transmission path may result in the following problems: in one aspect, the transmission bearing resources of carriers are wasted, resulting in an increase in operating costs; in another aspect, a delay in transmission and reception of IP packets between the MN1 and the MN2 is increased, which is not beneficial for improving the user's service experience; and in a further aspect, a large number of IP packets converge at the anchor LMA (usually an LMA can serve a number of MNs), which makes the LMA easily become a bottleneck of the performance, increases a possibility of congestion of the packets at the node, results in a decrease in the overall network quality, and results in the services of the MN being blocked or even impossible to implement (for example, real-time services such as voice, video etc.).
It should also be noted that when the MN1 and the MN2 are anchored on different local mobility anchors LMAs, reception and transmission of packets between the MN1 and the MN2 must be performed respectively via the anchors LMAs of the MN1 and the MN2. The roundabout waste of the packet transmission path is more obvious, and the above-described negative effects caused later are more severe.
In order to solve the waste problem of the transmission path existing in the PMIP mechanism and thus a series of resultant adverse consequences, there is a need to enhance the PMIP mechanism. FIG. 2 is enhanced PMIP protocol architecture.
Compared with the logical architecture of the PMIP protocol, network elements included in the ePMIP protocol architecture are a mobile node MN, an enhanced MAG (eMAG) and an enhanced LMA (eLMA).
As shown in FIG. 2, the eMAG1 is a first hop router of the MN1, and in addition to allocating a care of address CoA1 to the MN1 and substituting the MN1 to perform PMIP binding with the eLMA in the existing PMIP architecture, its primary functions further need to have the following functions (a first-hop router eMAG2 of the MN2 also has the same functions):
querying from the eLMA to acquire an address of the eMAG2 to which the communication node MN2 is currently connected or a care of address CoA2 of the communication node MN2;
establishing a bidirectional tunnel between the eMAG1 of the MN1 and the eMAG2 of the MN2, and forwarding IP data packets between the MN1 and the MN2; and
the eLMA retaining functions of processing registration, deregistration and update of the MN, a function of allocating the HNP, and functions of establishing and maintaining the BCE in the LMA functions. With respect to the LMA, the eLMA has the following enhanced functions:
the eLMA is not used as an anchor of data packets, and the IP packets between MN1 and MN2 needs not to pass through the eLMA.
The eLMA needs to respond to an address query request message from the eMAG.
FIG. 2 illustrates a path of reception and transmission of IP packets between the MN1 and the MN2 under the ePMIP architecture, i.e., MN1 and MN2<->eMAG1<->eMAG2<->MN2. The data packets directly pass through the tunnel between the eMAG1 and the eMAG2, without passing through the eLMA, thereby avoiding a series of problems due to roundabout of the transmission path.
To sum up, the ePMIP protocol well solves a series of problems existing in the conventional PMIP protocol, but upgrade to the existing conventional PMIP device will bring a great impact to the network, and increases a cost in network operations. Therefore, in the beginning of transition from the conventional PMIP to the enhanced ePMIP, in a operator network in which a PMIP is already deployed, it needs to deploy the ePMIP in an incremental manner without making any change to the conventional PMIP device. FIG. 3 illustrates a diagram of architecture of deployment of the ePMIP in a conventional PMIP domain in an incremental manner. For convenience of description, a PMIPv6 domain is divided into area1 and area2, in which ePMIP and PMIP are deployed. The MN11 and MN12 in the area 1 communicate in an ePMIP manner, with reference to the flow in FIG. 2, and all mobile nodes (MN21, MN22 and MN23) in the area2 communicate in a PMIP manner, with reference to the flow in FIG. 1.
As shown in FIG. 3, a conventional mobile access gateway MAG13 is deployed in the area1, and an MN13 registers with the eLMA through the MAG13. In this scenario, the MN13 and other mobile nodes (e.g., the MN11 and the MN12 illustrated in FIG. 3) which are attached under the eMAG can not communicate. By taking communication between the MN13 and the MN11 as an example, after downlink data transmitted from the MN13 to the MN11 arrives at the MAG13, the MAG13 forwards the downlink data using a conventional PMIP. However, after the uplink data transmitted by the MN11 to the MN13 arrives at the eMAG11, the eMAG11 queries a location from the eLMA, to acquire location information of the mobile access gateway MAG13 of the MN13. But as a tunnel cannot be established between the MAG13 and the eMAG11, the uplink data cannot be forwarded to the MN13.
In a handover scenario, in the process of communication between the MN11 and the MN12, the MN11 is handed over from the enhanced mobile access gateway eMAG11 located in the area1 to the mobile access gateway MAG21 located in the area2. As when the mobile node is handed over in the PMIP, the anchor does not change, a new mobile access gateway MAG21 must registers new location information of the MN11 with an enhanced local mobility anchor eLMA located in the area1. During handover, the downlink data transmitted from the MN12 to the MN11 will also be transmitted to eMAG11 through a tunnel between the eMAG12 and the eMAG11. However, as a tunnel can not be established between the eMAG11 and the MAG21, the eMAG11 cannot forward the downlink data to the MAG21, and then to the MN11, thereby leading to a handover packet loss in such handover scenario.
The problem of packet loss in the above two scenarios is to be solved.